(1) Field of the Invention
This invention relates to terpolymers of chlorotrifluoroethylene or tetrafluoroethylene, ethylene and perfluoroisoalkyloxy perfluoroalkyl ethylene. More particularly, this invention relates to such terpolymers having improved high temperature properties, in particular, improved resistance to thermal stress cracking.
(2) Prior Art
U.S. Pat. No. 3,738,923 describes copolymers of 40 to 60 mole percent of ethylene and from 40 to 60 mole percent of chlorotrifluoroethylene or tetrafluoroethylene. While copolymers of 40 to 60 mole percent of ethylene with 40 to 60 mole percent of tetrafluoroethylene, chlorotrifluoroethylene or mixtures thereof have high melting points, generally in the order of above about 200.degree. C., their use at temperatures above about 150.degree. C. has been severely restricted due to their tendency to stress-crack at such temperatures. At such temperatures they crack under tensile stresses appreciably below the limits of their short-term strength.
U.S. Pat. No. 3,847,881 discloses that the thermal stresscracking characteristics of copolymers of about 40 to 60 mole percent of ethylene with about 40 to 60 mole percent of halogenated comonomers selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene and mixtures thereof are improved by incorporating therein from 0.1 to 10 mole percent, based on the moles of halogenated comonomer, of 3,3,3-trifluoro2-trifluoromethylpropene.
U.S. Pat. No. 3,706,723 discloses that thermoplastic 3,3,3-trifluoro-2-trifluoromethylpropene/1,1-difluoroethylene copolymers are prepared by copolymerizing the monomers in liquid media in the presence of a free radical generating initiator. The copolymer products are melt-processable, retain their mechanical strength at high temperatures, and resist attack by corrosive agents and solvents.
U.S. Pat. No. 3,893,987 discloses that terpolymers may be formed by copolymerization of from about 0.1 to 30 mole percent of perhalogenated monomer selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene and mixtures thereof, and 3,3,3-trifluoro-2-trifluoromethyl propene/1,1-difluoroethylene copolymer, thereby improving its melt processing characteristics, without seriously deteriorating its good mechanical properties and chemical resistance. However, U.S. Pat. No. 3,893,987 further discloses that attempts to introduce ethylene as a third monomer into the copolymer failed to produce a terpolymer at low ethylene feed levels, but produced only a copolymer of 3,3,3-trifluoro-2-trifluoromethyl propane and ethylene at high ethylene feed levels and produced a terpolymer that decomposed before melting at intermediate ethylene feed levels.
U.S. Pat. No. 4,123,602 discloses that a terpolymer consisting of from 40 to 60 mole % of tetrafluoroethylene, 40 to 60 mole % of ethylene and 0.1 to 10 mole % of perfluoroalkyl vinyl component having the formula: EQU CH.sub.2 .dbd.CH--C.sub.n F.sub.2n+1
wherein n is an integer of 2 to 10, may be formed only if, throughout the course of the copolymerization, the molar ratio of C.sub.2 F.sub.4 to C.sub.2 H.sub.2 in the reactor is maintained essentially higher than 40 to 60 while keeping the mole % of the perfluoroalkyl vinyl monomer essentially in the range of from 0.1 to 10, based on the total monomer's content.
U.K Patent Application No. 2 084 593A discloses copolymers consisting of 93-99 mole % tetrafluoroethylene units and, complementally, 7-1 mole % fluorinated (C.sub.2 -C.sub.10)alkylethylene comonomer units and being characterized by having the units of the copolymer substantially uniformly positioned throughout the copolymer chain. The copolymers of the UK Patent Application are produced by copolymerization process wherein the fluorinated alkyl ethylene is uniformly added to the reaction vessel throughout the polymerization so as to maintain its concentration below 2.5 mole % relative to the tetrafluoroethylene.
U.S. Pat. No. 3,624,250 discloses that the high temperature tensile properties of a copolymer consisting essentially of chlorotrifluoroethylene or tetrafluoroethylene and ethylene are improved by incorporating therein a small amount of a vinyl monomer having the formulae: EQU R-CF.sub.2 .dbd.CF.sub.2 or ROCF.dbd.CF.sub.2 or R.sub.1 CH.sub.2 C(X).dbd.CH.sub.2 or R.sub.2 OCH.sub.2 C(X).dbd.CH.sub.2
wherein X is H or CH.sub.3. While use of vinyl monomers such as R.sub.1 CH.sub.2 C(X).dbd.CH.sub.2, wherein R.sub.1 is CF.sub.3 or CF.sub.3 CF.sub.2, and X.dbd.H, and perfluoroalkyl ethers (R.sub.2 OCH.sub.2 C(X).dbd.CH.sub.2), wherein R.sub.2 is perfluoroisopropyl and X.dbd.H is disclosed, working examples are only provided for perfluoroalkene-1 of the general structure R.sub.1 CF.dbd.CF.sub.2 and perfluorooxyl vinyl ethers (ROCF--CF.sub.2).
There is always a need for other comonomers which, when incorporated into copolymers of 40 to 60 mole percent of ethylene with 40 to 60 mole percent of chlorotrifluoroethylene, produce new copolymers of improved resistance to thermal stress-cracking and water vapor permeability and attack by common organic solvents, inorganic acids and bases at elevated temperature, without having significant adverse effect on thermal stability.